(Photo: Lars Chittka)
A round structure, no corners and edges – when we have seen a ball, we can then distinguish it from a cube simply by palpating it. As researchers have now found out, bumblebees are surprisingly capable of such a complex transfer of power between sensory systems: they can recognize a previously seen object simply by touching it and vice versa. This shows once again what complex cognitive functions the supposedly simple insect brains can produce, the researchers say.
The technical term is cross-modal perception: our brain stores information in a way that enables a connection with other senses. For example, we can feel a bunch of keys in a bag full of other things, because in our minds there is a mental picture of this object, which also includes how it feels. In addition to humans, this complex cognitive ability is only known from a few highly developed vertebrates. You might think that it is not worth looking for in insects. However, studies of recent years have impressively documented that these beings are not as simple as has long been assumed.
Amazingly clever insects
Above all, the bumblebee has proven its brains: The chubby cousins of the honeybees can therefore grasp relationships and solve tasks. In this context, it is known that they memorize visual and tactile features of objects that they perceive through their eyes or by touching them with the feelers. As part of their study, the researchers at Queen Mary University in London have now investigated whether bumblebees are capable of cross-modal perception in these two senses.
In the first attempt, they first taught their bumblebees to differentiate between balls and cubes solely by their sense of touch. The animals were presented with cube-shaped and spherical objects on petri dishes in a pitch-dark room. The balls had an opening that gave access to delicious sugar water. With the cubes, on the other hand, there was only one hideous bitter substance. As documented by recordings with infrared lighting, the bumblebees quickly learned to connect the shape with the reward by touching the structures with their feelers: they finally devoted their interest to crawling in the dark only to the balls, even if they contained no sugar water ,
The next step was the crucial one: the researchers presented the bumblebee with the balls next to the cubes in daylight. The objects were made inaccessible through a glass pane – the test animals could only see them and no longer feel them. The observations showed that the bumblebees deliberately buzzed around the balls and left the dice on the left. Accordingly, they could link what they saw with what they had previously only felt. In other words: Apparently something that feels round also looks round to a bumblebee.
A complex object image in the bumblebee head
Further experiments showed that this also applies in reverse. In the process, the bumblebees learned to distinguish the sight of balls and cubes in daylight without being able to use their sense of touch. During subsequent tests in the dark, they reacted with particular interest to the tactile stimuli of the balls and paid no further attention to the cubes. The shape did not play a fundamental role, the researchers emphasize: when they carried out their experiments with the cubes as reward objects, the bumblebees developed a cross-modal preference for this shape. “The results of our study show that bumblebees do not process their senses as separate channels – they unite them in a kind of overall representation,” sums up the first author of the study Cwyn Solvi.
She and her colleagues now see the results as further evidence of the long underestimated cognitive abilities of some insect species. “We have known for a long time that bumblebees can remember the shape of flowers. However, our work now also shows that mental images of these forms apparently arise in the brain of these insects, ”says co-author Lars Chittka. His colleague Selene Gutierrez Al-Khudhairy added: “This is an amazing achievement, considering the tiny size of the brains of these animals.”
Solvi warns, however, of overly humanized perspectives on the experience of the bumblebees, because it has so far been difficult to assess what exactly happens in the insects. She and her colleagues now want to address this aspect in further studies. “We do not say that bumblebees experience the world as we do, but our results at least show that something amazing is going on in their heads,” concluded Solvi.
Source: Queen Mary University, professional article: Science, doi: 10.1126 / science.aay8064